The general goal of the research is to understand and model the perception of visual spatial patterns by normal, human, adult viewers. The research proposed for the present period applies concepts and methods from the study of spatial pattern vision to the study of lightness and color constancy, with particular emphasis upon the role of spatial variables. there are four specific aims: (1) to give the problems of lightness and color constancy a formulation which facilitates manipulation of spatia variables and the application of concepts and models from the study of spatial vision; (2) to measure and compare the degree of constancy observed along three axes in tristimulus XYZ space, the cardinal directions of Krauskopf, Williams, and Heeley; (3) to assess the extent to which constancy is produced by early mechanisms which locally rescale the visual signal as some function of local mean radiance; (4) to examine the properties of the rescaling mechanism, particularly with respect to its multiplicative and subtractive properties and how it is affected by the spatial properties of the illumination and reflectance patterns. The proposed experiments are psychophysical and involve matching, discrimination, and detection.